1. Field of the Invention
This invention relates to a process for producing a cationic polymer and, more particularly, to a process for producing a water-soluble cationic polymer in a lump form.
2. Description of the Prior Art
A polymer derived from a vinyl monomer represented by the general formula (I) described hereinbelow is known as an excellent cationic flocculant and is widely used as a clarifying agent for domestic and industrial waste water or as a dehydration aid for organic sludge, e.g., as disclosed in Japanese Patent Publication No. 9534/58, U.S. Pat. Nos. 3,171,805, 3,414,513 and 3,414,514. Such a polymer is also used as an auxiliary in paper making, a textile treating agent, and a soil conditioner.
A number of methods for producing cationic polymers have heretofore been reported. One method, e.g., as disclosed in U.S. Pat. No. 3,099,636 and German Patent No. 1,153,174, comprises polymerizing a monomer in an aqueous solution in a concentration such that fluidity of the polymerization mixture still remains after completion of the polymerization, that is, at a water content of about 70% by weight or more, drying the polymerizate and grinding the dried polymerizate.
In another method, e.g., as disclosed in U.S. Pat. No. 3,509,113, the monomer is polymerized in an organic solvent using precipitation polymerization and then the organic solvent is removed. In still another method, e.g., as disclosed in Japanese Patent Application (OPI) No. 13,482/73 and U.S. Pat. No. 3,278,506, an aqueous solution of the monomer is suspended in an organic solvent and polymerization is carried out using suspension polymerization and the resulting polymer is separated from the organic solvent by filtration and then dried.
These methods, however, are not entirely satisfactory from an industrial standpoint, because drying equipment is required to remove a large quantity of water, the manufacturing expense is increased, or a large amount of an organic solvent is used which gives rise to the danger of fire and explosions.
In view of the above, extensive studies were conducted to develop a polymerization process for producing a powdered polymer without the necessity for drying the polymerizate or using an organic solvent and, as a result, it was found as disclosed in Japanese Patent Application No. 57434/1975 (corresponding to U.S. patent application No. 687298/76, filed, May 13, 1976) and now abandoned that is was possible to obtain on a commercial scale an easily grindable polymer in a lump form having excellent performance characteristics by polymerizing in bulk a vinyl monomer represented by the general formula (I) in the presence of a small amount of water.
While the polymerization process disclosed in Japanese Patent Application No. 57434/1975 is an improvement over the prior art methods described above, further improvements therein were found to be desirable. More specifically, the disclosure in Japanese Patent Application No. 57434/1975 is that care should be taken in handling the water-soluble cationic polymer produced, since this polymer generally has a very high adhesiveness or hygroscopicity.
This is also the case with polymers prepared from vinyl monomers represented by the general formula (I). If the polymerization vessel is composed of glass, stainless steel or the like which is generally used as a material for the polymerization vessel used in vinyl polymerization, the vinyl polymer obtained sticks so tenaciously to the polymerization vessel that it becomes extremely difficult to recover the vinyl polymer in the form of a lump or a sheet. Coating the glass or a metal surface with a silicone releasing agent or a mineral oil prior to polymerization may improve the tear characteristic (i.e. the ability to remove the polymer from the polymerization vessel) of the polymerization vessel to some extent, but even this method is not entirely satisfactory. The tear characteristic of the polymerization vessel can also be improved by lining the inner metal surfaces of the vessel with synthetic resins such as polytrifluorochloroethylene and polytetrafluoroethylene, but after repeated use of the polymerization vessel, the lining delaminates from the inner walls of the polymerization vessel so that the resulting polymer deposits on the bare walls and becomes difficult to recover from the polymerization vessel.
The polymerization vessel may be composed of polyethylene, polypropylene, polybutylene terephthalate, polycarbonate, polyethylene terephthalate used either alone or reinforced with glass fibers, but thermal expansion due to the heat of polymerization or shrinkage upon cooling causes a deformation of the polymerization vessel to occur, which then prevents easy separation of the resulting polymer from the polymerization vessel. These materials may be formed into a disposable polymerization vessel or a two-part polymerization vessel that allows removal of the polymer even if deformation occurs in the polymerization vessel, but neither type of polymerization vessel has been found to be entirely satisfactory for the industrial production of vinyl polymers from the standpoint of safety, durability and cost.
A polymerization vessel made of a plastic film and sealed against leakage has many advantages because such a polymerization vessel can be shaped into a bag, a tube or any other form, can be used as a disposable vessel for the relatively low cost of the plastic, and can be easily separated from the polymer. However, first of all, because the plastic film is thin, the plastic film is affected by external conditions such as temperature and atmosphere. Secondly, the kinds of the plastic films that can be used are limited because suitable plastics must have good thermal and mechanical characteristics. Thirdly, in actual production on an industrial scale involving complicated steps such as the step of forming a polymerization vessel and the step of tearing the resulting product off the polymerization vessel, certain precautions must be taken against leakage of the polymerization solution. Fourthly, no matter how low the cost is, use of the polymerization vessel only once with subsequent discard inevitably results not only in increased cost for the polymer product but also contributes to a waste of resources.
As explained above, a plastic polymerization vessel is not necessarily satisfactory for use in industrial production. On the other hand, metals which are heat resistant, have high form stability, and are relatively inexpensive may prove an advantageous material for a polymerization vessel.